The invention relates to a new process for preparing vinca alkaloids by reacting a product of catharanthine and vindoline type, characterised in that the reaction conditions are chosen so that vindoline is oxidised.
The invention relates to a process for preparing vinca alkaloids of the general formula (I) 
in which:
Rxe2x80x21 represents a hydrogen atom or an alkoxy, acyl, formyl or halogenoacyl group,
Rxe2x80x22 represents a hydrogen atom or an alkyl group,
Rxe2x80x23 and Rxe2x80x33 are identical or different and each independently represents a hydrogen atom or a hydroxyl or alkanoyloxyl group, or else Rxe2x80x23 and Rxe2x80x33 together form a carbonyl group or else Rxe2x80x23 and Rxe2x80x25 together form an epoxy bridge or a double bond,
Rxe2x80x24 represents a hydrogen atom or an alkyloxycarbonyl, hydroxymethyl or alkanoyloxymethyl group, preferably an alkyloxycarbonyl group,
Rxe2x80x25 and Rxe2x80x35 are identical or different and each independently represents a hydrogen atom or a hydroxyl, alkanoyloxyl, ethyl or 2-hydroxyethyl group,
Rxe2x80x26 represents a hydrogen atom or an ethyl, 2-hydroxyethyl or acetyl group,
Rxe2x80x27 represents a hydrogen atom or a cyanide group,
R1 represents a hydrogen atom or an alkyl, formyl or acyl group, preferably hydrogen or an alkyl group,
R2 represents a hydrogen atom or an alkoxy group,
R3 represents a hydrogen atom or a hydroxyl or alkanoyloxyl group, or else R3 and R4 together form an epoxy bridge or a double bond,
R4 represents a hydrogen atom or a hydroxyl or alkanoyloxyl group, or else R4 and R5 together form an epoxy bridge,
R6 represents an alkyloxycarbonyl, hydrazido, acetamido, hydroxymethyl or alkanoyloxymethyl group,
R5 and R7 represent a hydrogen atom or a hydroxyl or alkanoyloxyl group, as well as their addition salts with acids and their quaternary ammonium salts.
Some derivatives of the formula (I) are known as being intermediates in the preparation of anti-tumor medicaments such as vinblastine, vincristine and vinorelbine. 
R=CH3, vinblastine
R=CHO, vincristine
n=2, anhydrovinblastine
n=1, vinorelbine
The remarkable anti-tumor properties of these complex natural molecules, extracted from the Madagascar periwinkle, Carantheus roseus, are known and they are already used in anti-cancer treatment. Vinblastine and vincristine are xe2x80x9cspindle poisonsxe2x80x9d which oppose the formation of the mitotic spindle during cellular division, thus preventing cellular proliferation.
Vincristine and vinblastine are active agents in the treatment of leukemia, lymphosarcoma and solid tumors. Vinblastine is also used in the treatment of Hodgkin""s disease.
Vinorelbine is currently used in the treatment of the most widespread form of cancer of the lungs, that is lung cancer of non-small cells. It is also used in the treatment of metastasic cancers of the breast.
The methods currently used for preparing vinblastine and vincristine involve extraction of these molecules from plants. The plants have to be crushed and dried before these substances can be extracted. The extraction process is long and costly, given that the extract obtained is very complex, containing at least 200 different alkaloids. The yields are also very low; 5 to 10 g of vinoblastine are obtained per ton of dried plant material, and 0.5 to 1 g of vincristine per ton of dried plant material.
Many research groups have thus tried to achieve synthesis of these molecules by using more efficient procedures which enable better yields and which make use of derivatives with interesting anti-tumor properties but which are endowed with lower levels of toxicity.
The patent FI 882 755, filed by the HUATAN-MAKI Oy Company, relates to the formation of vinblastine and vincristine by irradiation of catharanthine and of vindoline with UV radiation in an acidic aqueous solution, under an atmosphere of oxygen or an inert gas. The yields obtained in these reactions are extremely low.
Furthermore, other processes are known which make use of anhydrovinblastine which is an intermediate in the synthesis of vinblastine, vincristine and also of vinorelbine.
Anhydrovinblastine is thus a key chemical intermediate which enables access to all alkaloids of the vinblastine type. This intermediate is synthesised by coupling catharanthine and vindoline. 
The latter two alkaloids are also extracted from the Madagascar periwinkle but, in contrast to vincristine and vinblastine, they represent the main constituents of the extract obtained. In fact, 400 g of catharanthine per ton of dried plant material and 800 g of vindoline per ton of dried plant material are obtained.
The preparation of anhydrovinblastine by coupling catharanthine and vindoline is therefore a favoured route for synthesising this intermediate product.
There are several methods for preparing anhydrovinblastine from catharanthine and vindoline.
The patent FR 2 296 418 filed by ANVAR describes a process during the course of which the N-oxide of catharanthine is coupled to vindoline in the presence of trifluoroacetic anhydride.
When this process is performed at ambient temperature only the inactive 16xe2x80x2-R epimer of anhydrovinblastine is obtained. The naturally occurring active 16xe2x80x2-S epimer is obtained as the major product when this reaction is performed at a temperature which is at least 50xc2x0 C. lower and under an inert gas. Nevertheless, even at low temperature, 10% of the 16xe2x80x2-R epimer of anhydrovinblastine is still produced.
This process has several disadvantages. The operating conditions are extremely restrictive due to the use of anhydrous solvents, the low temperature and the atmosphere of inert gas. The product obtained has to be subjected to a purification procedure due to the presence of 10% of the 16xe2x80x2-R epimer of anhydrovinblastine. The yield of isolated anhydrovinblastine is low, of the order of 35%.
A second process, suggested by VUKOVIC et al. in the review xe2x80x9cTetrahedronxe2x80x9d (1998, volume 44, pages 325-331) describes a coupling reaction between catharanthine and vindoline initiated by ferric ions. Catharanthine is also oxidised in this reaction. The yield of anhydrovinblastine is of the order of 69% when the reaction is performed under an atmosphere of inert gas. However, this process has the major disadvantage that it leads to many secondary products. These are impurities resulting from further oxidation of the dimeric alkaloids formed, whatever the chosen operating conditions. This makes the purification stage difficult and delicate.
An improved process was suggested in the patent U.S. Pat. No. 5,037,977 and this increases the yield of anhydrovinblastine to 89%. However, this improvement is described only for very small amounts of reagents and its extension to the industrial scale seems to be difficult. In any case, these processes based on ferric ions lead in all cases to many secondary products due to the fact that these ions are responsible for parasitic reactions.
A third process described by GUNIC et al. in xe2x80x9cJournal of the Chemical Society Chemical Communicationsxe2x80x9d (1993), volume 19, pages 1496-1497, and by Tabakovic et al. in xe2x80x9cJournal of Organic Chemistryxe2x80x9d (1997), volume 62, pages 947-953, describes a coupling reaction between catharanthine and vindoline as a result of anodic oxidation of catharanthine. However, this process also suffers from disadvantages which, on the one hand, are due to the requirement for an inert atmosphere and, on the other hand, are connected with the nature of the electrochemical process itself, involving wear of the electrodes, difficulty in controlling the reproducibility and the cost of electrolytes. And, as in all the preceding methods, the anhydrovinblastine is contaminated with about 10% of the 16xe2x80x2-R epimer of anhydrovinblastine.
It should be noted that all the processes disclosed hitherto, without exception, involve splitting open the catharanthine molecule, this being induced by oxidation or activation of the latter. These processes are performed under restrictive conditions and do not permit satisfactory yields of a sufficiently pure product.
The process according to the invention permits the production of vinca alkaloids of the general formula (I) and in particular of anhydrovinblastine, by making use of less restrictive operating conditions, with excellent yields and high purity. The process according to the invention permits the production of anhydrovinblastine in its naturally occurring active form, without any trace of the 16xe2x80x2-R epimer of anhydrovinblastine.
The present invention thus relates to a process for preparing a product (A) corresponding to the general formula (I) 
in which:
Rxe2x80x21 represents a hydrogen atom or an alkoxy, acyl, formyl or halogenoacyl group,
Rxe2x80x22 represents a hydrogen atom or an alkyl group,
Rxe2x80x23 and Rxe2x80x33 are identical or different and each independently represents a hydrogen atom or a hydroxyl or alkanoyloxyl group, or else Rxe2x80x23 and Rxe2x80x33 together form a carbonyl group, or else Rxe2x80x23 and Rxe2x80x25 together form an epoxy bridge or a double bond,
Rxe2x80x24 represents a hydrogen atom or an alkyloxycarbonyl, hydroxymethyl or alkanoyloxymethyl group, preferably an alkyloxycarbonyl group,
Rxe2x80x25 and Rxe2x80x35 are identical or different and each independently represent a hydrogen atom or a hydroxyl, alkanoyloxyl, ethyl or 2-hydroxyethyl group,
Rxe2x80x26 represents a hydrogen atom or an ethyl, 2-hydroxyethyl or acetyl group,
Rxe2x80x27 represents a hydrogen atom or a cyanide group,
R1 represents a hydrogen atom or an alkyl, formyl or acyl group, preferably hydrogen or an alkyl group,
R2 represents a hydrogen atom or an alkoxy group,
R3 represents a hydrogen atom or a hydroxyl or alkanoyloxyl group, or else R3 and R4 together form an epoxy bridge or a double bond,
R4 represents a hydrogen atom or a hydroxyl or alkanoyloxyl group, or else R4 and R5 together form an epoxy bridge,
R6 represents an alkyloxycarbonyl, hydrazido, acetamido, hydroxymethyl or alkanoyloxymethyl group,
R5 and R7 represent a hydrogen atom or a hydroxyl or alkanoyloxyl group,
as well as their addition salts with acids and their quaternary ammonium salts, by reacting a product (c) corresponding to the general formula (II): 
in which Rxe2x80x21, Rxe2x80x22, Rxe2x80x23, Rxe2x80x33, Rxe2x80x24, Rxe2x80x25, Rxe2x80x35 and Rxe2x80x26 are defined as above, with a product (v) corresponding to the general formula (III): 
in which R1, R2, R3, R4, R5, R6 and R7 are defined as above, this process being characterised in that the reaction conditions are chosen such that product (v) is oxidised in order to obtain an intermediate (i) of the general formula (IV): 
in which R1, R2, R3, R4, R5, R6 R7 and Rxe2x80x21, Rxe2x80x22, Rxe2x80x23, Rxe2x80x33, Rxe2x80x24, Rxe2x80x25, Rxe2x80x35 and Rxe2x80x26 are defined as above, and in that the product (i) of formula (IV) is subjected either to reduction or to cyanation in order to obtain product (A) of formula (I).
Product (v) can be oxidised using any known means. The following may be mentioned by way of example: photochemical, organometallic and electrochemical routes. Product (v) is preferably oxidised using the photochemical route in the presence of light and optionally an organic or inorganic sensitizer.
The inorganic sensitizer may be a transition metal or a semi-conductor, preferably being a ruthenium complex or titanium oxide.
The organic sensitizer is a colorant, preferably chosen from the group consisting of xanthates, pyriliums, pyridiniums, flavines, aromatic compounds, ketones and quinones as well as their salts, in particular chosen from among fluorescein, triphenylpyrilium, 4-(4-methoxy-phenyl)-2,6-diphenylpyrilium, 2,6-bis-(4-methoxyphenyl)-4-phenyl-pyrilium and 2,4,6-tris-(4-methoxyphenyl)-pyrilium.
The oxidation step is performed in an acidic medium, preferably at a pH between 0 and 7, in particular between 0.5 and 3.
The reduction stage for product (i) may be performed by any known means. An alkaline borohydride is preferably used, in particular sodium borohydride.
The cyanation step for product (i) may be performed by any known means. This step is preferably performed in an organic medium in the presence of a source of cyanide ions which are not alkaline, or are slightly alkaline, in particular in the presence of trimethylsilyl cyanide.
In fact, the applicant Company has discovered that choosing the reaction conditions in such a way as to oxidise product (v) (and not product (c) as in the prior art), leads to a stereospecific reaction with respect to the C16 carbon atom in intermediate (i), thus avoiding contamination by the inactive 16xe2x80x2-R epimer. Moreover, this stereospecificity is independent of the temperature of the reaction medium, thus simplifying the method of preparation.
When (v) is oxidised via the photochemical route, the light used is within the UV/visible spectrum, preferably greater than 254 nm and in particular greater than 400 nm.
The invention also relates to a process for preparing anhydrovinblastine by reacting catharanthine with vindoline, this process being characterised in that the reaction conditions are chosen in such a way that vindoline is oxidised in order to obtain an intermediate (ixe2x80x2) of the formula (V): 
and in that the intermediate (ixe2x80x2) of formula (V) is subjected to reduction in order to obtain anhydrovinblastine.
The invention also relates to novel products (B), corresponding to formula (VI): 
in which:
Rxe2x80x21 represents a hydrogen atom or an alkoxy, acyl, formyl or halogenoacyl group,
Rxe2x80x22 represents a hydrogen atom or an alkyl group,
Rxe2x80x23 and Rxe2x80x33 are identical or different and each independently represents a hydrogen atom or a hydroxyl or alkanoyloxyl group, or else Rxe2x80x23 and Rxe2x80x33 together form a carbonyl group, or else Rxe2x80x33 and Rxe2x80x25 together form a double bond,
Rxe2x80x24 represents a hydrogen atom or an alkyloxycarbonyl, hydroxymethyl or alkanoyloxymethyl group,
Rxe2x80x25 and Rxe2x80x35 are identical or different and each independently represents a hydrogen atom or a hydroxyl, alkanoyloxyl, ethyl or 2-hydroxyethyl group,
Rxe2x80x26 represents a hydrogen atom or an ethyl, 2-hydroxyethyl or acetyl group,
R1 represents a hydrogen atom or an alkyl, formyl or acyl group,
R2 represents a hydrogen atom or an alkoxy group,
R3 represents a hydrogen atom or a hydroxyl or alkanoyloxyl group, or else R3 and R4 together form an epoxy bridge or a double bond,
R4 represents a hydrogen atom or a hydroxyl or alkanoyloxyl group, or else R4 and R5 together form an epoxy bridge,
R6 represents an alkyloxycarbonyl, hydrazido, acetamido, hydroxymethyl or alkanoyloxymethyl group,
R5 and R7 represent a hydrogen atom or a hydroxyl or alkanoyloxyl group.
These are new derivatives of vinca alkaloids in which there is a cyanide group attached to the carbon in position 21xe2x80x2. These products have the advantage of being readily functionalised, thus enabling the production of new molecules which are of potential interest at the cytotoxic level.
These products (B) can be functionalised either by nucleophilic compounds or by electrophilic compounds.
In addition, the invention relates to a new product (D) of the formula VII: 
This is a derivative of anhydrovinblastine, that is to say 21xe2x80x2xcex1-cyanoanhydrovinblastine. In fact, the applicant Company has developed a process for manufacturing 21xe2x80x2xcex1-cyanoanhydrovinblastine, a molecule which can readily be functionalised and thus permits the production of novel derivatives which are of potential interest at the cytotoxic level.
21xe2x80x2a-cyanoanhydrovinblastine can be functionalised either by nucleophilic compounds or by electrophilic compounds. Thus, the range of potentially accessible derivatives is very large.
This new compound (D) is also very interesting because it is relatively stable, which enables it to be isolated and obtained in the pure, crystalline form. The advantage of obtaining crystals of a precursor of derivatives is that functionalisation reactions of this precursor can be performed in a clean reaction medium, free of all traces of reactive residues.
21xe2x80x2xcex1-cyanoanhydrovinblastine enables the production of derivatives which are mono or polysubstituted at positions C15xe2x80x2, C20xe2x80x2 and C21xe2x80x2 in anhydrovinblastine or these derivatives.
The invention also relates to a process for preparing 21xe2x80x2xcex1-cyanoanhydrovinblastine by reacting catharanthine with vindoline, this process being characterised in that the reaction conditions are chosen in such a way that vindoline is oxidised in order to obtain an intermediate (ixe2x80x2) of the formula (V) and in that the intermediate (ixe2x80x2) is subjected to cyanation in order to obtain product (D).
Cyanation is preferably performed in an organic medium in the presence of a source of cyanide ions which are not alkaline, or are slightly alkaline, for example trimethylsilyl cyanide.
The invention will be better understood with the aid of the non-restrictive examples which follow.